Messages in this thread | | | Date | Mon, 2 May 2016 19:41:14 +0200 | From | Oleg Nesterov <> | Subject | Re: GUP guarantees wrt to userspace mappings redesign |
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On 05/02, Kirill A. Shutemov wrote: > > On Mon, May 02, 2016 at 06:22:11PM +0200, Oleg Nesterov wrote:
> > > So we have pages pinned by a driver and the driver expects the pinned > > > pages to be mapped into userspace, then __replace_page() kicks in and put > > > different page there -- driver's expectation is broken. > > > > Yes... but I don't understand the problem space. I mean, I do not know why > > this driver should expect this, how it can be broken, etc. > > > > I do not even understand why "initiated by other process" can make any > > difference... Unless this driver somehow controls all threads which could > > have this page mapped. > > Okay, my understanding is following: > > Some drivers (i.e. vfio) rely on get_user_page{,_fast}() to pin the memory > and expect pinned pages to be mapped into userspace until the pin is gone. > This memory is used to communicate between kernel and userspace.
Thanks Kirill.
Then I think uprobes should be fine,
> I don't think there's something to fix on uprobe side. It's part of > debugging interface. Debuggers can be destructive, nothing new there.
Yes, exactly. And as for uprobes in particular, __replace_page() can only be called of vma->vm_file and and the mapping is private/executable, VM_MAYSHARE must not be set.
Unlikely userspace can read or write to this memory to communicate with kernel or something else.
Thanks,
Oleg.
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